GB 1,299,481 shows a plate evaporator of the above kind. Evaporation liquid flows towards the evaporation spaces inside a channel which is defined in part by the aligned openings that form the passage through the heat transferring plates. Each of the distribution chambers are in restricted liquid flow communication with at least one evaporation space, by means of narrow flow ways/small through holes formed in the heat transferring plates or in the aforementioned seals, as shown in FIG. 1b of GB 1,299,481, whereby the liquid flows over the surfaces defining the evaporation spaces in the form of a falling film. Through the size of the flow ways/through holes it may be ensured that about the same amount of liquid flows from the channel and into the individual evaporation spaces along the entire length of the channel.
It is a problem with such plate evaporators that particles suspended in the liquid may lead to a clogging of the aforementioned flow ways, affecting the falling film of liquid. In addition, due to the low rate of flow in the individual distribution chambers sedimentation of the suspended particles may also occur in the distribution chambers. Simply increasing the size of the flow ways/through holes to a size that still provides for a falling film may be desirable to reduce clogging; however, making the through holes larger may cause a relatively larger amount of the liquid to flow into those evaporation spaces that are located closest to the inlet, thereby reducing the overall efficiency of the evaporator.
Attempts to avoid clogging have been made by arranging filters upstream of the plate evaporator. However, in some applications space constraints and/or the nature of the liquid to be evaporated are such that clogging can still not be prevented, even if a filter of some kind is provided. One example is desalination applications where the plate evaporator is used on board a ship or similar places where available space for high grade filters is limited, and where the liquid to be evaporated is sea water. In coast-near areas sea water may contain silt having a particle size of 5-10μ; the sea water may also contain algae of the same particle size. Algae passing through even a fine mesh filter has a tendency to agglomerate, and such agglomerates have often been found to be the cause of clogging, requiring a time consuming and costly dismantling and cleaning of the heat transferring plates.